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Fish can recognise one human face from another, according to new research.

A species of tropical fish was able to distinguish between human faces, the first time fish have shown such an ability.

The research, by scientists from Oxford University plus the University of Queensland in Australia, found that archerfish were able to learn and recognise faces with a high degree of accuracy.

An archerfish in its aquarium at a laboratory in OxfordCredit:
Caitlin Newport/AFP

The researchers said it is an "impressive" feat, given that it requires sophisticated visual recognition capabilities.

Dr Cait Newport, of Oxford University, said: "Being able to distinguish between a large number of human faces is a surprisingly difficult task, mainly due to the fact that all human faces share the same basic features.

"All faces have two eyes above a nose and mouth, therefore to tell people apart we must be able to identify subtle differences in their features.

"If you consider the similarities in appearance between some family members, this task can be very difficult indeed.

"It has been hypothesised that this task is so difficult that it can only be accomplished by primates, which have a large and complex brain.

An archerfish spittingCredit:
Caitlin Newport/AFP

"The fact that the human brain has a specialised region used for recognising human faces suggests that there may be something special about faces themselves.

"To test this idea, we wanted to determine if another animal with a smaller and simpler brain, and with no evolutionary need to recognise human faces, was still able to do so."

The researchers found that fish, which lack the sophisticated visual cortex of primates, are still capable of discriminating one face from up to 44 new faces.

The fish continued to spit at the face they had been trained to recognise, proving that they were capable of telling the two apartDr Cait Newport, Oxford University

In the study, published in the journal Scientific Reports, archerfish - a species known for its ability to spit jets of water to knock down aerial prey - were presented with two images of human faces and trained to choose one using their jets.

The fish were then presented with the learned face and a series of new faces and were able to correctly choose the face they had initially learned to recognise.

They were able to complete the task - even when more obvious features, such as head shape and colour, were removed from the images.

The fish were highly accurate when selecting the correct face, reaching an average peak performance of 81 per cent in the first experiment - picking the previously learned face from 44 new faces, and 86 per cent in the second experiment in which facial features such as brightness and colour were standardised.

Dr Newport said: "Fish have a simpler brain than humans and entirely lack the section of the brain that humans use for recognising faces.

"Archerfish are a species of tropical freshwater fish that spit a jet of water from their mouth to knock down insects in branches above the water.

"We positioned a computer monitor that showed images of human faces above the aquariums and trained them to spit at a particular face.

"Once the fish had learned to recognise a face, we then showed them the same face, as well as a series of new ones.

"In all cases, the fish continued to spit at the face they had been trained to recognise, proving that they were capable of telling the two apart.

"Even when we did this with faces that were potentially more difficult because they were in black and white and the head shape was standardised, the fish were still capable of finding the face they were trained to recognise.

"The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognise human faces.

"Humans may have special facial recognition brain structures so that they can process a large number of faces very quickly or under a wide range of viewing conditions."

Human facial recognition has previously been demonstrated in birds. But, unlike fish, they are now known to possess neocortex-like structures.